A Fossil Thermometer

Smithsonian Institution, Smithsonian Institute

In this activity, students calculate temperatures during a time in the geologic record when rapid warming occurred using a well known method called 'leaf-margin analysis.' Students determine the percentage of the species that have leaves with smooth edges, as opposed to toothed, or jagged, edges. Facsimiles of fossil leaves from two collection sites are examined, categorized, and the data is plugged into an equation to provide an estimate of paleotemperature for two sites in the Bighorn Basin. It also introduces students to a Smithsonian scientist who worked on the excavation sites and did the analysis.

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Notes from our reviewers

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Need to encourage students to really look at the leaves and not just play with the interactive tool. Another activity with a stronger coverage of the science: [http://www.ucmp.berkeley.edu/IB181/VPL/Clim/Clim1.html]
Students are required to examine leaf edges using either large poster images or an online interactive tool and do some simple arithmetic to understand the differences in the leaves from different sites. This activity gives an example of how scientists themselves conduct their inquiry. Large amount of background information appropriate for educators and students is available. References to the original data, as well as that for the correlations between mean temperature and leaf morphology, are not included. An article addressing the underlying science of leaf margin analysis can be found here: Wilf, Peter. (1997). When are leaves good thermometers? A new case for Leaf Margin Analysis. Paleobiology, 23(3), 373-390 . Ideally the change seen during the early Cenozoic should be related with any effects that it had on biota. The explanation of the term "isotopes" is provided, educators need to clarify this in class. Comment from scientist: When used immediately following "Cenozoic," the term "era" should possess an uppercase "E" (i.e., Cenozoic Era).